1. Field of the Invention
The present invention relates to a wireless tag capable of acquiring information detected by a built-in sensor, a wireless tag reader/writer, a wireless tag information provision method, and a wireless tag system.
2. Description of the Related Art
Along with development of information communication technology, the trend has set in to perform commodity management or to streamline the commodity information display or the commodity distribution by packaging a Radio Frequency (RF) tag having an integrated circuit with memory [generally, sometimes called as electronic tag, contactless data carrier, wireless IC tag, contactless IC, contactless IC label, contactless IC tag, RFID (Radio Frequency Identification) or NFC (Near Field Communication) tag] in articles and recording various types of information in the RF tag. The RF tag performs wireless communication with a RF tag reader device which reads information such as an identification code stored in the memory incorporated in the RF tag. Hereafter, the RF tag shall be referred to as “wireless tag”.
Wireless tags having various types of built-in sensors have recently been drawing attention. The wireless tags with built-in sensors are employed in various systems. As an example of such systems, a perishable food management system suitable for characteristics and distribution mode of perishable foods has been proposed (see Japanese Laid-Open Patent Publication No. 2002-358591, paragraphs 0058-0060 (hereafter, Patent Publication 1), for example).
The system described in Patent Publication 1 is a system for managing preservation quality when storing and transporting perishable foods. According to this system, a tag includes a temperature sensor for detecting temperature, an impact sensor for detecting impact, a memory for storing data detected by the temperature and impact sensors, a transceiver for transmitting the data in the form of extremely low radio waves, and an identification number adding portion for adding an identification number unique to the tag to the data, and such tag is enclosed in a package containing perishable foods. A tag receiver for receiving data transmitted from the tag is installed in the vicinity of the place where the package is stored, and the tag receiver is connected to communication equipment which utilizes a communication circuit or wide area wireless networks. An information collection center is installed for collecting data on the tags from the communication equipment. The information collection center determines the preservation quality of the perishable food in each package based on a history of preservation environment indicated by the collected tag data, and informs the preservation quality to a terminal which makes an inquiry to the information collection center via a communication circuit Preservation environment determination means is further provided at least in any of the tag, a transport vehicle, and the information collection center for determining whether the preservation environment is good or not based on the data detected by the sensors in comparison with a predetermined threshold, and informing the determination result to the transport vehicle transporting the tag.
In addition to this conventional system, there have been proposed temperature sensors, temperature measurement devices, temperature measurement systems and programs utilizing a wireless tag having a rewritable mass data storage area (see Japanese Laid-Open Patent Publication No. 2004-144683, paragraphs 0017-0018 (hereafter, Patent Publication 2), for example).
A temperature sensor described in Patent Publication 2 is configured as a wireless tag having a resonant circuit the resonant frequency of which varies depending on temperature. The resonant circuit is composed of a coil and a capacitor. A material the dielectric constant of which varies according to variation in temperature is provided between electrodes of the capacitor. The wireless tag has a memory, communication means, and a microcomputer. The memory stores resonant frequency versus temperature characteristics of the resonant circuit as a table. The microcomputer transmits and receives radio waves via the communication means while changing the frequency to specify a resonant frequency of the resonant circuit, and specifies temperature corresponding to the resonant frequency by referring to the table. The microcomputer periodically specifies the resonant frequency and the temperature, and records the temperatures thus specified in the memory as a history. The microcomputer retrieves the temperature history stored in the memory in response to a command received via the communication means, and transmits the same via the communication means. The temperature measurement device described in Patent Publication 2 includes detection means for detecting a resonant frequency of the resonant circuit by transmitting and receiving radio waves to and from a wireless tag having a resonant circuit the resonant frequency of which varies depending on temperature, specifying means for specifying temperature of the wireless tag based on the detected resonant frequency, receiving means for receiving settings of monitoring temperature by the user, control means for controlling the detection means and the specifying means to periodically specify the temperature, determination means for determining whether or not the specified temperature has reached the monitoring temperature, and alarm means generating an alarm when it is determined that the specified temperature has reached the monitoring temperature.
There has also been proposed an electronic tag system which is able to shorten the processing time by periodically transmitting transmission information to record history information in a plurality of electronic tags, while simultaneously causing the system's internal information to be processed in parallel (see Japanese Laid-Open Patent Publication No. 2005-25240, paragraphs 0070-0075 (hereafter, Patent Publication 3), for example).
An electronic tag system described in Patent Publication 3 has a contactless electronic tag and a reader/writer for contactless electronic tags. The reader/writer includes common accessing means for accessing a plurality of contactless electronic tags in common, and means for transmitting information to the contactless electronic tags with the use of the common accessing means. The contactless electronic tag has means for receiving information provided by the common accessing means, computation means, storage means, and means for transmitting a response to the reader/writer or means for storing the computation result of the computation means in storage means. The computation means includes means for determining a response by using the information provided by the common accessing means and the information stored in the storage means.